Elements of Network Connectivity Serial and Parallel communication Modems Modem Pools ISDN DSL Routing Cable systems Leased Lines Other interconnection systems

Serial vs. Parallel Serial –needs one wire plus return per direction –bits are sequenced by time slicing –needs synchronization –needs handshaking codes or lines Parallel –all bits sent at one time –needs 1 wire per bit –needs handshaking lines

Serial Frame (Async) Time Start Stop Word= Hex=5C Ascii= \

Serial Frame (Synchronous) Bit No start or stop bits, timing synchronized with special ascii characters (SYN) c07dem13 and c07dem14 Time

Parallel Bits 6 7 Strobe Time Pulse

Serial Communications Serial Data Stream (asynchronous) –8 bits data –start/stop bits –Parity bit –baud rate –limits –Errors –c07dem10

Serial Communications RS-232 standard Modems PC Serial Ports Speeds Synchronous/Asynchronous –Advantages/Disadvantages PPP (Point to Point Protocol)

RS232 Standard 25 ping connector 9 pin connector Ground Transmit Receive Clear to Send Request to Send Carrier Detect Data Set Ready Data Terminal Ready Ring Detect 0 volts +3 to 25 Volts -3 to 25 Volts

Modem Operation Modulator/Demodulator (Digital to Analog) Use a standard (Hayes) command set. Dialup Sequence Training/Speed Negotiation –Error detect and compression/decompression –Latest and greatest (??) is V.90 (56KB) Carrier Detect Requirements for 56K xDSL (Digital Subscriber Line) ISDN (digital telephone lines)

PPP Primer Point to Point protocol Physical Layer protocol Authentication (PAP/CHAP) Addressing (dynamically assigned) Client Configuration

Modem Pools Requirements ISDN BRI lines (single connection) ISDN PRI (23 BRI) lines (equal a T1) Tariffs (QWest) Multiplexing BRI’s to save $$ Central Office Switch Line selection/hunting

PPP Installation Modem Controller Ethernet $52.50 per line Modems

56K (ISDN) Modem Installation Central Office Ethernet T1’s or ISDN PRI Controller $33.50 per line

ISDN Handles Voice, Data, Video Each BRI (Basic Rate Interface) has 2 64 Kbps lines, either can be used for data or voice, combined gives 128 Kbps data. BRIs and PRIs (Primary Rate Interface) –BRI 64 Kbps, 128 Kbps –PRI 1544 Kbps (23 BRIs) Dial up standard –Each line has a phone number

DSL Asymmetric Digital Subscriber Line Asymmetric (High speed downlink, slow uplink) Uses existing telephone cabling to the DSL modem router Modem/router typically provides ethernet connection to your LAN Uses existing telephone devices for voice (single twisted pair) Simultaneous data and voice Distance limitation from central office (12000 feet)

DSL Digital Subscriber Link –ADSL Asymmetric DSL –xDSL foot radius of Central Office Speeds to 1,544 KB downstream –640 kbps upstream Simultaneous voice/data Uses existing telephone twisted pair

More DSL HDSL High Speed DSL –2 Mbps at 3 miles of cable VDSL Very High Speed DSL –52 MBS downstream, MBS upstream –3000 foot limit SDSL Symmetric DSL –1.544 MBps up and down, foot limit

Even More DSL Pricing: $45/month and up dsl/index.html Requires: –Telephone line (POTS) –DSL Modem –External Modem requires Ethernet to the PC

Routing Routers operate at the Network layer They use tables to keep track of the best path from source to destination They segment the network based on Network layer traffic They filter broadcast traffic to a single port on the router Routers listen on the ports and determine the best path using OSPF (open shortest path first), RIP (Routing Information Protocol), or NSLP (NetWare Link Services Protocol) for IPX

Routing Continued Some protocols don’t route: –Netbeui –Local Area Transport (DEC) Routers can be either: –Static, addresses to other routers are fixed –Dynamic, addresses to other routers are discovered automatically. Routers can use multiple links to another site to take advantage of available bandwidth on each link.

Gateways Gateways are like routers but switch between protocols Example: –Token-Ring to ethernet –IBM HDLC/SNA to Internet TCP/IP Because of the switching algorithms needed they are usually slow.

Radio and Satellite Bandwidth versus available frequencies High Power and Broad Bandwidth requires FCC licensed equipment Interference (electrical, atmospheric, animal) Timing problems ( 1 foot = 1 ns.) –23500 miles to satellite (.25 sec round trip)

Cable TV modems Use existing cable installation Uses broadband network technology via fiber optics and coaxial cable Asymmetric (8 MB down/1 MB up) Costs about $40.00/month

RAS Remote Access Service –NT interconnection system –Can use several different media including dialup –Can filter specific protocols, it can audit connections and use Callback security. –Works up to about 128 kbps.

Telco Leased Line Networks ISDN DSL T1, DS1, T3, DS3 –T1 is Mpbs –Interfaces, CSU/DSU, Framing –CSU/DSU Channel Service Unit/Data Service Unit OC1, OC3, OC12 –Optical Circuits, OC1 is Mbps, OC3 is Mbps

Leased Lines DS-1/T Mbps or 24 voice channels DS3/T Mbps (28 T1s), 672 voice Packet Switched –Uses best route –Uses small packets Virtual Circuit Packet Switching –Bandwidth Allocated on demand –SVC (Switched Virtual Circuit) –PVC (Permanent Virtual Circuit)

Frame Relay Fast, variable length, packet switching network. Uses PVCs for point to point communication Provides customers with variable rate bandwidth, customers share bandwidth with other customers.

ATM (Asynchronous Transfer Mode) Used for high speed data communications primarily by common carriers (Telco). Uses cell relay rather than variable length frames ATM is expensive and fairly complicated to set up and troubleshoot.

FDDI Fiber Distributed Data Interface Dual Ring (Token ring topology) –Redundant (Fault Tolerant) Handles long distances (because of fiber) –200 kilometers (124 miles) –immune to electromagnetic noise/interference 100 Mbps Protocol includes built in troubleshooting Interfaces are fairly expensive

SONET (Synchronous Optical Network) Fiber Optic Gigabit communications protocol. Standard for long distance high speed transport of data and voice Basic transmission unit is STS-1 at Mbps up to STS-192 or 9, Mbps